The evolution of wireless communication over the past century, since Guglielmo Marconi's 1897 demonstration of radio's ability to provide continuous contact with ships sailing the English Channel, has been remarkable. Since Marconi's discovery, new wireline and wireless communication methods, services and standards have been adopted by people throughout the world. This evolution has been accelerating, particularly over the last ten years, during which the mobile radio communications industry has grown by orders of magnitude, fueled by numerous technological advances that have made portable radio equipment smaller, cheaper and more reliable. The exponential growth of mobile telephony will continue in the coming decades as well, as this wireless network interacts with and eventually overtakes the existing wireline networks.
In 1982, the Groupe Special Mobile (GSM) committee took the initiative of developing standards for a European cellular telephony system in a 900 MHZ band. The resulting standard was named GSM, after its developers. A first level of GSM specifications was approved by the European Telecommunications Standards Institute (ETSI) in 1990 and a second level of recommendations was issued at the end of 1993. In the ensuing years, the GSM standard has been implemented in more than thirty-six networks in over twenty countries. The GSM standard continues to evolve and has recently been revised to operate in a newly reserved frequency band in the 1800 range in Europe and in the 1900 range in North America. The revised GSM standard is also known as Personal Communication Services 1900 or PCS 1900. FIG. 1 illustrates the typical components of a GSM wireless communications system 8.
The GSM wireless communications system 8 is located within a geographical area serviced by a single provider called the public land mobile network (PLMN). The basic components of the wireless communications system 8 are a base station system 10, a mobile service switching center (MSSC) 12 and terminal equipment (TE) 14. At least one base station system 10 is deployed within the PLMN. The base station system 10 acts as an interface between the MSSC 12 and the terminal equipment 14. The terminal equipment 14 may be mobile wireless telephones, pagers or other equipment. The terminal equipment 14 in GSM includes a subscriber identification module or SIM card 22 which is plugged into the terminal equipment 14. The SIM card 22 allows the subscriber to access the network through any terminal equipment 14 in which the subscriber has inserted their SIM card 22. The SIM card 22 includes such data as a unique subscriber identity and encryption keys, telephone number, list of preferences in networking, charging information and other data.
The base station system 10 includes a base transmission station 18 and base station controller 20. The base transmission station 18 operates as a transceiver for transmitting and receiving data and control messages to and from the terminal equipment 14 over the air interface. The air interface includes both traffic and control channels. The traffic channels transmit voice or data at various rates. A full rate traffic channel allows the transmission of speech coded at 13 kbits/s or asynchronous and synchronous data at various user transmission rates, up to 14.4 kbits/s. The control channels are used to control call processes and provide information. Various control channels include, inter alia, a broadcast control channel (BCCH) that periodically transmits base station identification and parameters, a paging channel (PCH) to call a terminal to initiate a call process, and a standalone dedicated control channel (SDCCH) to exchange information before a traffic connection, and a random access channel (RACH) for a request from the terminal to initiate an exchange of information. The control channels and traffic channels may be mapped into the allowed frequency band in various ways.
The base station system 10 is connected to the MSSC 12 through dedicated telephone lines at an A interface 30. Also connected to the MSSC 12 is a visitor location register (VLR) 24 and a home location register (HLR) 16. The VLR 24 is a database used to store data for any terminal equipment 14 which has registered within the service area of the particular MSSC 12 and though shown as a separate node is often implemented within the same node or server as the MSSC 12. The HLR 16 is a database which stores subscriber information for all subscribers to that PLMN. An interworking function unit (IWF) 32 in the MSSC 12 links the wireless communications system 8 to the public switched telephone network (PSTN) 26 via a trunk 28. Alternatively, the PSTN network 26 may be an integrated services digital network (ISDN). The functions related to switching and networking are generally controlled by equipment located above the A interface 30. Thus, the MSSC 12 and IWF 32 control the switching of incoming calls to various base station systems 10 and the interfacing of outgoing calls to the PSTN or ISDN network 26.
The wireless communications system 8 provides wireless telephony services as well as bearer services and other services available through the PSTN network 26. The concept of an ISDN was first formulated by a division of the International Telegraph Union (ITU) called the International Consultative Committee for Telephone and Telegraph (CCITT). ISDN was meant to provide user access to the integrated digital network (IDN) of digitized switching and transmission. CCITT has provided extensive coverage of the ISDN network 26 in various series of standards, including G (Transmission), Q(Switching and Signaling), and the V series. In Europe, the ITU standard V.110 is commonly used to communicate between two computers. ITU V.110 protocol is used end-to-end between the two computers and is part of a terminal adapter unit connected to the computer, in the same manner as a modem. The terminal adapter (TA) provides bit rate adaption and end-to-end synchronization. The GSM system uses a modified ITU standard across the air interface. The modified GSM system's version of the ISDN service is designated V.110'.
The basic bearer services offered in the European market of the ITU V.110 are based on data channels having an unrestricted bearer services of 64 kbps data rate. The trunks 28 between an ISDN network 26 and a wireless communications network 8 are typically operating at unrestricted data rates of 64 kbps in the European market.
In North America, the corresponding ISDN services are typically based on a somewhat similar ITU standard designated V.120. Due to different recommendations promulgated by the American National Standards Institute (ANSI), some trunks 28 in the United States may provide data rates of 56 kbps with 8 kbps of the channel reserved for control signaling. This is called channel associated signaling (CAS). Also, an intermediate case is in use where signaling is carried out of band but a High-Level Data Link Control (HDLC) inverted mode is used to keep synchronization. These two modes are commonly called restricted 64 kBit/s transfer capability because less than 64 kBits/s of data are transferred. Thus, the physical links 28 in the United States may comprise both restricted digital information (RDI) of less than 64 kbits/s and unrestricted digital information (UDI) equal to 64 kbits/s.
Currently, ETSI is studying having access to ISDN services in Europe and North America and on compatibility with CCITT recommendations. ETSI is standardizing interworking between the GSM V.110' and ITU standard V.120 for European PLMN operators, i.e., wherein a European PLMN operator is transmitting or receiving ISDN messages to and from the United States. These recommendations are reported in ETSI Publication GSM 09.07, entitled, "Digital cellular telecommunications system (Phase 2+); General requirements on interworking between the Public Land Mobil Network (PLMN) and the Integrated Services Digital Network (ISDN) or Public Switched Telephone Network," (December 1996).
However, ETSI has provided no guidance or technical documentation describing the interworking between a GSM system operating with ISDN services under the GSM V.110' standard and an ISDN system operating under the ITU standard V.120 when the PLMN operator is operating a GSM system in North America or other markets where data rates other than the unrestricted transfer capability of 64 kbps is provided in the physical trunks. For example, the ETSI publication GSM 09.07 assumes that the ISDN network connected to the wireless communications network 8 provides a 64 kbps data link.
Additional guidance is needed in this area due to the differences in the physical link data rates between North America and Europe. Thus, a need has arisen for a system and method to govern the interworking of a GSM wireless communications system with an ITU V.120 standard ISDN network which is operating under the ANSI standards of physical links with restricted data rates of less than 64 kbits/s.
Similarly, there is no documentation describing interworking between the two ITU standards V.110 and V.120. Thus, a need has also arisen for a system and method to govern the interworking between an ISDN network operating in accordance with ITU V.110 and another ISDN network operating in accordance with ITU V.120.
It is, therefore, an object of the present invention to provide a system and method for such interworking between diverse transfer capability networks.